Force measuring device



Sept. 8, 1942. H. BROWN Erm.

I FORCE MEASURING DEVICE Filed June 5, 1959 HART BRW/V JQHN H. MRT/N y INVENroR.

BY @ZM/f". Y

ATTORNEY `Patented Sept. 8, 1.942

UNITED STATESv4 PATENT Y OFFICE f 'v 2,295,026Y

. FORCE MEASURING DEVICE [Hart Brown and John II. Martin, Houston, Tex.`

` Application June 5, 1939, Serial No. 277,514

` 7 claims. The invention relates Ato instruments for measuring variations in a force and is of particular utility in the field of gravimetric measurements in the art of geophysical prospecting for subterranean structures favorable to the lo`cation of valuable deposits. M

An object of this invention is to arrange a mass suspended by a multiiilar torsion-tension suspension system in such a manner that the sensitivity of the system to desired forces can be adjusted to high values, and such that the sensitivity of the system to undesirable forces and to undesirable oscillations can be minimized.

It is also an object to provide a force responsive instrument whichis capable of measuring changes in the magnitude of a force regardless of the nature of such force.

Another `object is to provide an instrument which'is capable of measuring minute changes in force with an extremely vhigh degreev of accuracy.

A particular object of the invention is to use a multilar torsion-tension suspension system consisting of three strands, the ends of which are supported nonlinearly so as to limit lthe degrees of freedom of the suspended mass and thus to minimize unwanted oscillations of that mass.

Still another object is to provide a device havbodying the invention, y

Fig.`2 is a side elevational view of thecon-l the' mass, and means for developingtor'sion inY Veach of the three strands so that the mass is ro- -tated until it approaches a point of unstable equilibrium. thereby constituting an instrument of high sensitivity and one `which issuitable for gravimetri'c measurements.

One form which this invention takes whenonly three strandsare used and in which symmetry is featured, will be apparent from the, following description taken in connectionfwith the drawing in which: 4

Fig. 1 is a plan view of the'constructio'n emstruction shown in Fig. 1. i n

Fig. 3 is a plan View similar to that shown in e Eig.v 1 but illustrating the relative position of ing a multilar suspension in which supporting strands are arranged about a common point in the force responsive system.

Still another object is to provide a measuring instrument for measuring* changes in gravimetric force by the effect produced by such force on a gravity responsive member supported by a plurality of suspension torsion strands attached thereto.

A more specific object is to provide an instrument including a support and a force responsive member, the latter being supported by a plurality of suspension-torsion strands the ends of which are attached to the supporting member and the force responsive member in non-linear array about a point in each of such members, means being provided for subjecting some or all of the strands to torsion whereby differential displacement of the force responsive member is a measure of theA change in the force producing such displacement. Y v

Astill more specic object is to provide ,an instrument including a support, to which are fastened three strands positloned symmetrically about and equi-distant from a central point, a mass to which the lower end of the strands are attached at three points symmetrically located about and equi-distant from a central point on parts when torsion isapplied to the strands supporting the'force responsive member.

Fig. 4 is aside elevationalview ofthe construction shown in Fig. '3.

Fig. 5 is a plan view of a spider type of force,l responsive member.

Fig. 6 is a fragmentary view illustrating an alternate manner ofv attaching the suspensiontorsion strands tothesupport. 4

Since the invention isl of primary. utility in measuring small changes in the force of gravity, it will be described in connection with the ymaking of `such measurements altho it is to be understood that such description is illustrative only as the invention contemplates an instrument which is capable of measuring, with extreme accuracy, changes in theforce whether such force be magnetic, electrostatic, gravimetric vor* otherwise or a combination ,of such forces.

In providing such a device the illustrated embodiment of the invention comprises a support member I. This memberis stationary and is provided with a plurality of knobs 2 which are rotatably mounted thereon and which are provided vwith stems 3 extending a part or all of the way f wardly therefrom.,` These strands may be of metal or other suitable material, as for example quartz,

and'may comprise ribbons, rods, tubes, or otherstructural shapes kof suchmaterial, the principal requisite being that they shall possess desired,

characteristics including sufficient tensile and torsional strength that the instrument will effectively serve the purpose for which designed.

are attached to I vwhereby a very slight be accurately determined. Alternately,

The lower ends of the strands 6 are attached to a mass or gravity responsive member 1 which is shown inFigs. 2 and 4 as a disc. In this particular embodiment of this invention, the three tion is not confined thereto but broadly comprehends inequalityiniR and r and either may be the larger.

Any one or all of the knobs 2 are rotated, for example, in a clockwise direction asvindicated by the arrows I in Fig. 1, the gravity responsive member 1 will rotate thru an angle a as indi- 1lik in the strand. 'I'his undesirable feature may be avoided in accordance with the fragmentary view of' Fig. 6, wherein the knob"2 and its associated stem are shown as rotatably mounted in the supporti in alinement with the strand 8 which exten-ds in the direction assumed when the instrument is adjusted for normal operation.

The mode of operation of the described construction seems apparent but reference will be made thereto by way of summary directed to the use of the instrument in the determination of small changes of gravimetric force a. The knobs 2 are turned suiilciently that the member 1 is rotated thru an angle a to acquire the desired sensitivity. Suitable vclamping means are provided (not shown) for holding the member 1 in a ilxed position during transportation of the instrument so as to avoid undesirableeilects that would result from any impacts to which the incated in Fig. 3. It is obvious that the angle a v will depend upon the summation of the torques applied by the strands 6. `iit the same time the member 1 will be lifted an increment dh and the'v relative position of parts' will then be as shown in Fig. 4. y

`If suiilcint torque be applied to the strands 6 the angle a will become sufficiently great that a `rcondition of unstability is approached. lIi then the force tending to return the member 1 to a lower position varies by a small amount,`a material change in the rotational deection of the member 1 will take place. This 'change in deiiection is indicated as @a in Fig'. 3 of the drawing and the amount of this-differential deiiection is a measurement of the change in the force acting upon the member 1 and producing such Change.`

The change in the force may obviously be determined by the angular deflection 9a'. Other methods and devicesmay, however, be relied upon for obtaining the desired' data. For example an indication of the change in dh may be utilized or,

strument might be subjected.

A datum point is establishedV by unclamping the member 1 and observing the deflection at that point. The instrument is successively clamped 'during transportation between other points in an area to be prospected. At each point of observation the change eiected by the change in gravity of that point from' the established point is noted and nnally a check observation is made upon the initially established point v in order to ascertain any trend which may have taken place in the instrument. By making observations at a. suitable numberv of. points within the area of prospecting, a contour map may be drawn, such map a null'method of making observations may be utilized. This may be accomplished thru a force exerted by mechanical means or by an electrcstatic or magneticvforce acting upon the member 1 andaof suiiicient amplitude to return the member to a null position. The amount of the restoring force necessary to4 eiect such movement of the gravity responsive' member 1 is thus ya measure of the 'change in force causing the member `tofdeviate from the null position.

The gravity responsive member 1, illustrated as a disc, may be madein various other forms such as a ring or a spider,as shown as 1' in Fig. 5. In vthis embodiment .the lower ends of the strands are attachedat the points l0. Mounted centrally of the member 1f is shown a mirror il which may be utilized to provide an optical lever "angular movement may of course, the mirror may be used when accurately return- `ing the member 1' to the null position as above described.

When the instrument is adjusted for `normal operating conditions each of the strands 6 ex- 'tends diagonally downwardfrom its supporting stem 3. If then for purposesof adjustment the torsion inthe'strand is to be increased or decreased the rotation of the knob 2 for such adjustmet will effect the desired change. During rotation of the knob 2, however,l the strand is caused to flex at its point of attachmentto' the stem-3. Such fiiexure sets up undesirable stresses indicating from the gravimetric' measurements` the location and extent structures. l

.Altho the form of the invention described above calls for three torsion-tension strands, the invention may bey practiced by the'use. ofthree or more such strands. Likewise this construction may carry equal torsion and/or equal tension as is the case where a yperfectly symmetrical arrangement is used but this equality of tension or torsionisnot a necessary condition to the practice of the invention. Also the strands which of anomalous subsurface are used may all be of the same material-but they may be of diiIerent materials. For example certain `advantages accrue from the use of strands having differenttorsion constants and itis intended that the invention shall include such prac- In the preferred Aembodimentillustrated as describedthe strands l are shown of yuniform length. Again it is to lie-understood that such proportioning, of parts is not `necessary to the practice of the invention.

'I'he knobs 2 have lbeen shown arranged. symmetrically about the point 4, that is.120 apart, and each at adistance R from the central point. Altho this symmetrical arrangement has certain advantages itis also to bedistinctly understood that the invention may be practiced with `asymmetrical arrangement in order to take 'advantage of the benets resulting from the asymmetry.

Such departure from the speciiic disclosure also applies to the arrangement of the points of attachment to the force responsive member 1.

Broadly the invention comprehends a means of measuring small increments of force, auch instrument comprising a force responsive member which is supported by a multiiilar suspension of tension-torsion strands which are so arrayed as to minimize unwantedosciliations of the mov ing system and which atthe same time provides an instrument having a sumcie'ntly highv degree of accuracy to measure minute changes in the force to be measured.

What is claimed is:

1. A force measuring device comprising a support, a trilar suspension comprising three rotatable members mounted on the support symmetrically about a point thereon, a suspension strand' carried axially of each of said members, and a. force responsive member supported by said strands, certain of said strands beingtwisted whereby the force responsive member is rotated to a position of equilibrium by the torque.

2. A force measuring device comprising a support, a trilar suspension comprisng three strands attached to the support in non-linear spaced relation, a force responsive member 'supported by the strands, and means for developing a torsional force in each of the strands whereby the force responsive member is rotated through Aan angle which is a measure of the forces acting on the member.

3. A device of the character described comprising a support, a plurality of members rotatably mounted thereon in nonlinear spaced relation, a suspension-torsion strand attached to each of said rotatable members, and a force responsive member attached to said strands and supported thereby, whereby the force responsive member is rotated to a position of equilibrium determined by the forces acting on such member.

4. An instrument for measuring variations in the value of the acceleration of gravity comprising a mass, at least three suspension strands supporting said mass at separate points on a horizontal plane, said points being located at the vertices of a regular polygon having its center at the intersection between said plane and a vertical line passing through the center of gravity of said mass,`and means for twisting each of said strands.

5. An instrument for measuring variations in the value of the acceleration of gravity comprising a mass solely and substantially equally supported by three suspension strands of substantially equal length and physical properties at points in the same horizontal plane and equidistant from each other, a support, and three members rotatably mounted on said support, each of said members having the upper end of one of said strands axially aixed thereto and being located so that said strands when free from torsional stress assume substantially vertical positions.

6. An instrument for measuring variations in the value of the acceleration of gravity comprising a mass, at least three suspension strands supporting said mass at separate points on a horizontal plane; said points being located at the vertices of a regular polygon having its center at the intersection between said plane and a vertical line passing through the center of gravity of said mass, and means for twisting each of said strands.

7. An instrument for measuring variations in the value of the acceleration of gravity comprising a mass solely and substantially equally supported by three suspension strands of substantially equal length and physical properties at points in the same horizontal plane and equidistant from each other, a support, and three members rotatably mounted on said support, each of said members having the upper end of one of said strands axially aiiixed thereto and being located so that said strands when free from torsional stress assume substantially vertical positions. y

HART BROWN.

JOHN H. MARTIN. 

